Display device

ABSTRACT

In a display device having a display region formed by disposing a plurality of organic light emitting elements such as organic EL elements, it becomes possible to prevent penetration of water into the display region to suppress degradation in display characteristics even during drive over a long period of time and to improve long-term reliability. There is provided a display device comprising a display region  120  having a plurality of organic light emitting elements disposed on a substrate  101 , each of the plurality of organic light emitting elements having an organic layer  103  comprising a light emitting layer interposed between an anode and a cathode ( 102, 104 ), wherein the display region  120  is formed on a first insulating protective layer  106  provided on the substrate  101 , and a surface on a side opposite to a substrate  101  side and an entire periphery of the display region  120  are covered with an insulating protective film  107.

TECHNICAL FIELD

The present invention relates to a display device and, moreparticularly, to a display device which uses an organic light emittingelement such as an organic electroluminescent element as a displayelement, and which is suitable for an active-matrix organicelectroluminescent display or the like.

BACKGROUND ART

Organic electroluminescent elements using electro-luminescence(hereinafter referred to as EL) of an organic material are formed bystacking organic layers, i.e., an organic carrier transport layer and anorganic light emitting layer, between an anode and a cathode, andattract attention as a light emitting element capable of high-luminanceemission by low-voltage direct-current drive.

The development of active-matrix display devices having thin-filmtransistors (hereinafter referred to as TFTs) for driving organic ELelements for pixels among display devices using the above-describedorganic EL elements has been pursued particularly energetically byconsidering their high-image-quality and long-lifetime characteristics.

FIG. 5 is a schematic perspective view of an active-matrix organic ELdisplay device. Display pixels 502 are disposed in a matrix form on asubstrate 501, and a pixel circuit for driving an EL element for eachpixel is contained. A drive circuit 503 for driving each pixel is alsocontained on the periphery of the array of the pixels. These circuitsare constituted by TFTs and wiring and are connected to externalcircuits through external lead terminals 504 to be driven. Ordinarily,upper surfaces of the pixel portion 502 and the drive circuit 503 arecovered with a sealing member 505 such as a glass or metal plate bondedto the substrate 501 by an adhesive 506 to maintain a mechanicalstrength.

In the display device thus constructed, a flattening insulating film isprovided in a state of covering the TFTs and wiring provided on thesubstrate, and organic EL-elements are provided on this flatteninginsulating film. The organic EL elements and the wiring are connected toeach other via contact holes formed in the flattening insulating film.

As an example of the flattening insulating film, one formed by applyinga resin material such as polyimide by spin coating is used as disclosedin Japanese Patent Application Laid-Open No. H10-189252 (patent document1).

With this display device, however, there is a problem described below.

That is, the flattening insulating film formed by application such asspin coating has a high water absorbing property because it is mademainly of an organic material or contains an organic material. Forexample, a water absorption coefficient of a polyimide film formed byapplication of a commercially available coating liquid is up to 1 to 3%.Since the light emitting portion of the organic EL element used as adisplay element is made of an organic material, a disadvantage such as areduction in luminance intensity or an increase in drive voltage canoccur easily therein by absorption of water. In a case where a materialhaving a high water absorbing property is used as the flatteninginsulating film as described above, therefore, water gradually releasedfrom the flattening insulating film seriously affects the displayperformance of the display element, resulting in failure to enable thedisplay device to have long-term reliability. Because degradation of thedisplay element by absorption of water proceeds even during the processof manufacturing the display device, the release of water from theflattening insulating film is also a cause of a reduction in yield ofthe display device.

To solve the above-described problem, an arrangement such as disclosedin Japanese Patent Application Laid-Open No. 2001-356711 (patentdocument 2), for example, has been proposed in which a coat layer 6 bmade of an inorganic material is formed on the surface of a flatteninginsulating layer 6 a as a barrier against water released from an organicmaterial constituting the flattening insulating layer 6 a and otherimpurity gas components (see FIG. 6).

In the display device shown in FIG. 6, TFTs 2 of the bottom gate type(which may alternatively be of the top gate type) are provided in amatrix form on a substrate 1 made of a glass material, for example, andan insulating film 3 is formed in a state of covering the TFTs. On thisinsulating film 3, wiring 4 connected to the TFTs 2 via connection holesnot illustrated is provided on the insulating film 3.

On the insulating film 3 is also provided an interlayer insulating film6, the wiring 4 being embedded in the interlayer insulating film 6. Theinterlayer insulating film 6 is provided in a multilayer structureformed of a flattening insulating layer 6 a and a coat layer 6 bprovided on the flattening insulating layer 6 a. The flatteninginsulating layer 6 a is formed of a material obtained by using anorganic material such as SOG (Spin-on-Glass) or a resin material (e.g.,a polyimide resin, an acrylic resin, or an organic silica film). Theflattening insulating layer 6 a is an applied film formed by anapplication method such as spin coating. The coat layer 6 b is formed byusing an insulating material having a gas barrier property such as to becapable of limiting the release of a gas from the flattening insulatinglayer 6 a . An inorganic material such as silicon oxide, silicon nitride(Si₃N₄), amorphous silicon (α-Si) or aluminium oxide (Al₂O₃) is used toform the coat layer 6 b in a single-layer or multilayer structure. Thecoat layer 6 b has such a film thickness as to be capable ofsufficiently effectively suppressing the release of a gas from theflattening insulating layer 6 a.

In the interlayer insulating film 6 formed in such a multilayerstructure, connection holes 7 reaching the wiring 4 are provided. Sideperipheral walls of the connection holes 7 are covered with the coatlayer 6 b , and the upper surface of the flattening insulating film 6 aand the surface facing the interior of each connection hole 7 arecompletely covered with the coat layer 6 b.

Organic EL elements 10 are provided on the interlayer insulating film 6in a state of being connected to the wiring 4. The organic EL elements10 are, for example, of an upper-surface emission type such that anemitted light radiates from the side opposite to the substrate 1 sideand are each constituted by a lower electrode 11 connected to the wiring4 via the connection hole 7, an insulating layer 12 provided in a stateof covering a peripheral edge of the lower electrode 11, an organiclayer 13 provided on the lower electrode 11, and an upper electrode 14and a transparent electrode 15 provided on the organic layer 13. Theorganic EL elements 10 may alternatively be of a transmission type suchthat light is taken out from the substrate 1 side.

The device is thus arranged to suppress the release of water from theflattening insulating film to the organic EL elements and to preventdegradation of the organic EL elements due to absorption of water duringdrive over a long time period.

(Patent document 1)

-   Japanese Patent Application Laid-Open No. H10-189252    (Patent document 2)-   U.S. patent application Publication No. US2002/036462A1

Even an arrangement such as shown in FIG. 6 also has a problem describedbelow.

As described above, the arrangement shown in FIG. 6 is effective inpreventing penetration (or permeation) of water into the upper organicEL elements from the flattening insulating film (indicated by arrow 21in FIG. 6). In designing the actual device construction, however, otherwater penetration paths that should be considered exist, and which arealso shown in FIG. 6. That is, penetration of water from the flatteninginsulating film at a display region end surface (indicated by arrow 22in FIG. 6), penetration of water from contacting atmosphere (indicatingarrow 23 in FIG. 6), penetration of water from contacting atmospherefrom the upper surface of the display region (indicated by arrow 24 inFIG. 6) and the like are taken into consideration. Further, theinterpixel insulating layer 12 formed between adjacent pixels for thepurpose of preventing short-circuit between the lower (pixel) electrodesand the upper electrodes is made mainly of an organic material orcontains an organic material, as does the flattening insulating film.Therefore there is a need to prevent penetration of water from theinterpixel insulating film as well as through the flattening insulatingfilm (indicated by arrow 25 in FIG. 6). However, as is seen from theabove description of the prior art, no measures have been taken againstpenetration of water through these paths in the above-describedarrangement.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished in consideration of theabove-described problems, and it is an object of the present inventionto prevent, in a display device having a display region formed bydisposing a plurality of organic light emitting elements such as organicEL elements, penetration of water into the display region to suppressdegradation in display characteristics even during drive over a longperiod of time and to improve long-term reliability.

According to the present invention, there is provided a display devicecomprising a display region having a plurality of organic light emittingelements disposed on a substrate, each of the plurality of organic lightemitting elements having an organic layer comprising a light emittinglayer interposed between an anode and a cathode,

wherein the display region is formed on a first insulating protectivelayer provided on the substrate, and a surface on a side opposite to asubstrate side of the display region and an entire periphery of thedisplay region are covered with an insulating protective film (or coat).

In the present invention, it is preferred that a flattening insulatingfilm with a substantially flat surface is disposed between the firstinsulating protective layer and the substrate; a second insulatingprotective layer is provided between the flattening insulating film andthe substrate; and an entire periphery of the flattening insulating filmis covered with an insulating protective film (or coat).

In the present invention, it is further preferred that at least one ofthe anode and the cathode is divided in a matrix form; anelement-separating portion for isolating at least adjacent ones of thediscrete electrodes is formed between the adjacent electrodes; and anelement-separating portion covering layer is provided between theelement-separating portion and the organic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a first embodiment ofthe present invention;

FIG. 2 is a schematic cross-sectional view showing a second embodimentof the present invention;

FIG. 3 is a schematic cross-sectional view showing a third embodiment ofthe present invention;

FIG. 4 is a schematic cross-sectional view showing a fourth embodimentof the present invention;

FIG. 5 is a schematic perspective view of an active-matrix organic ELdisplay device; and

FIG. 6 is a schematic cross-sectional view of a conventional displaydevice using organic EL elements.

BEST MODE FOR CARRYING OUT THE INVENTION

The display device of the present invention will be described withreference to the drawings. However, the present invention is not limitedto forms described below.

First Embodiment

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, asubstrate on which TFTs, wiring, etc., (not shown) are formed isindicated by 101. Pixels (organic EL elements) constituting a displayregion 120 are constituted by pixel electrodes 102 (having electricalconnections not shown in FIG. 1 to the TFTs) divided in a matrix form,organic layers 103 including light emitting layers constituting organicEL elements, a counter electrode 104, and element-separating portions105 disposed between the pixel electrodes. In this embodiment, thecounter electrode 104 is formed as a common electrode for all theorganic EL elements.

In this embodiment, glass was used as the substrate, patterned Cr wasdisposed in a matrix form as the pixel electrodes provided as anodes ofthe organic EL elements, and ITO (indium-tin oxide) was used as thecounter electrode provided as a cathode of the organic EL elements. AnSiO₂ film was grown and patterned to form the element-separatingportions. The materials of the substrate, the anode electrodes, thecathode electrode and the element-separating portions and the reversedpositions of the anode and cathode are not essential to the presentinvention, and this combination is not exclusively used. For example,the inorganic insulating film of SiO₂ is used as the element-separatingportions, however, SiN film may alternatively be used or an organicinsulating film, e.g., a film of photosensitive polyimide or acrylicresin or a resin film having no photosensitivity may be used. A resinfilm having no photosensitivity is formed by etching and patterning witha resist patterning mask or the like. In a case where an organic resinfilm is used as the element-separating portions, use of such a film ismade more effective if means for preventing penetration of water throughthe film is provided as described below.

In FIG. 1, a first insulating protective layer is indicated by 106 andan insulating protective film is indicated by 107. These films areprovided in such a structure that the film 106 is formed below the pixelelectrodes 102 and the element-separating portions 105, the film 107 isformed above the counter electrode 104, and the upper and lower surfacesand all the side surfaces of the display region 120 constituted by theplurality of organic EL elements are completely covered with these twoprotective films.

The adoption of this arrangement made it possible to suppresspenetration of water from contacting atmosphere surrounding the displayregion (in correspondence with arrows 23 and 24 in FIG. 6), to suppresspenetration of water into the organic EL elements during drive over along time period, and to prevent degradation of the organic EL elementdue to absorption of water.

Second Embodiment

FIG. 2 shows a second embodiment of the present invention. The samereference characters indicate components equivalent in function to thoseshown in FIG. 1. In comparison with the first embodiment, thisembodiment has a flattening insulating film 108 provided on thesubstrate 101 to reduce irregularities in the substrate surface. As theflattening insulating film, a film formed by applying a polyimide resinmaterial spin coating as described with respect to an example of theconventional art was used.

In this embodiment, the first insulating protective layer 106 is formedbetween the flattening insulating film 108 and the display region 120and a second insulating protective layer 109 as another insulatingprotective layer is formed between the flattening insulating film 108and the substrate 101. The insulating protective film 107 formed on thecounter electrode 104 is formed so as to cover peripheral areas of thedisplay region 120 and end surfaces of the flattening insulating film108.

The adoption of this arrangement made it possible to suppresspenetration of water from contacting atmosphere surrounding the displayregion (indicated by arrows 23 and 24 in FIG. 6) and penetration ofwater released from the flattening insulating film end surfaces(indicated by arrow 22 in FIG. 6), to suppress penetration of water intothe organic EL elements during drive over a long time period, and toprevent degradation of the organic EL element due to absorption ofwater.

The second insulating protective layer 109 was further formed betweenthe flattening insulating film 108 and the substrate 101 to eliminatethe influence of water, etc., on the elements including the TFTs formedon the substrate, thus improving the operation reliability.

Third Embodiment

FIG. 3 shows a third embodiment of the present invention. The samereference characters indicate components equivalent in function to thoseshown in FIG. 1. In comparison with the first embodiment, thisembodiment has an element-separating portion covering layer 110 providedon the upper surfaces of the element-separating portions 105.

The adoption of this arrangement made it possible to suppresspenetration of water from contacting atmosphere surrounding the displayregion (indicated by arrows 23 and 24 in FIG. 6) and penetration ofwater released from the element-separating portion surfaces (indicatedby arrow 25 in FIG. 6), to suppress penetration of water into theorganic EL elements during drive over a long time period, and to preventdegradation of the organic EL element due to absorption of water.

Incidentally, in the case where an organic resin film is used as theelement-separating portions and the element-separating portion coveringlayer in accordance with the present invention is provided, theelement-separating portion covering layer may be provided at leastbetween the element-separating portions and the organic layers. However,the device can easily be manufactured if it is provided in such a formthat, as shown in FIG. 3, the electrodes 102 divided in a matrix formare disposed on the first insulating protective layer 106, theelement-separating portions 105 are disposed so as to cover the gapbetween adjacent electrodes and portions of the divided electrodes toisolate adjacent electrodes from each other, and the element-separatingportion covering layer is formed on the element-separating portions in astate of reaching the electrodes. Also, this form is preferable becauseof its effectiveness in preventing penetration into the organic layersof water contained in the element-separating portions.

Fourth Embodiment

FIG. 4 shows a fourth embodiment of the present invention. The samereference characters indicate components equivalent in function to thoseshown in FIG. 1. In comparison with the first embodiment, thisembodiment has a flattening insulating film 108 provided on thesubstrate 101 to reduce irregularities in the substrate surface. As theflattening insulating film, a film formed by applying a polyimide resinmaterial spin coating as described with respect to an example of theconventional art was used.

In this embodiment, the first insulating protective layer 106 is formedbetween the flattening insulating film 108 and the display region 120and a second insulating protective layer 109 as another insulatingprotective layer is formed between the flattening insulating film 108and the substrate 101. Further, the insulating protective film 107formed on the counter electrode 104 is formed so as to cover peripheralareas of the display region 120 and end surfaces of the flatteninginsulating film 108. Further, the element-separating portion coveringlayers 110 are formed on the upper surfaces of the element-separatingportions 105.

The adoption of this arrangement made it possible to suppresspenetration of water from contacting atmosphere surrounding the displayregion (indicated by arrows 23 and 24 in FIG. 6), penetration of waterreleased from the flattening insulating film end surfaces (indicated byarrow 22 in FIG. 6) and penetration of water released from theelement-separating portion surfaces (indicated by arrow 25 in FIG. 6),to suppress penetration of water into the organic EL elements duringdrive over a long time period, and to prevent degradation of the organicEL element due to absorption of water.

The second insulating protective layer 109 was further formed betweenthe flattening insulating film 108 and the substrate 101 to eliminatethe influence of water, etc., on the elements including the TFTs formedon the substrate, thus improving the operation reliability.

In the above-described first to fourth embodiments, films such as thefirst insulating protective layer 106, the insulating protective film107 and the element-separating portion covering layer 110 were formed insuch a form as to contact the pixel electrodes 102, the organic layers103 and the element-separating portions 105 that form the displayregion. However, an insulating film with no possibility (or an extremelylow possibility) of releasing water, e.g., an inorganic insulating filmmay exist between these layers.

Although in the above-described embodiments the second insulatingprotective film 109 formed in a region below the flattening insulatingfilm 108 was formed in such a form as to contact the flatteninginsulating film 108, the present invention is not limited to theabove-described form as long as the flattening insulating film 108 iscovered.

In the display device of the present invention, it is preferable toadopt an arrangement in which the display region is covered with atransparent member such as a glass member to maintain a mechanicalstrength. In such a case, the transparent member such as a glass membermay be bonded to the substrate with a suitable space left therebetweenor may be directly bonded to the insulating protective film 107. In thecase of direct bonding, the influence of penetration of water fromexternal air shown in FIG. 6 (by arrow 24) can be further reduced.

As the first insulating protective layer 106, insulating protective film107, second insulating protective layer 109 and element-separatingportion covering layer 110 of the present invention, an inorganicmaterial such as silicon oxide, silicon nitride (Si₃N₄), amorphoussilicon (α-Si) or aluminium oxide (Al₂O₃) can be favorably used.

With the display device of the present invention, as described abovewith respect to the embodiments, a display region constituted by organiclight emitting elements such as organic EL elements is covered withinsulating protective films for preventing penetration of water tosuppress degradation of display characteristics during drive over a longtime period and to improve long-term reliability.

1. A display device comprising a display region having a plurality oforganic light emitting elements disposed on a substrate, each saidorganic light emitting element having an organic layer comprising alight emitting layer interposed between an anode and a cathode, whereinthe display region is formed on a first insulating protective layerprovided on the substrate, and a surface on a side opposite to asubstrate side of the display region and an entire periphery of thedisplay region are covered with an insulating protective film.
 2. Thedisplay device according to claim 1, wherein a flattening insulatingfilm with a substantially flat surface is disposed between the firstinsulating protective layer and the substrate; a second insulatingprotective layer is provided between the flattening insulating film andthe substrate; and an entire periphery of the flattening insulating filmis covered with an insulating protective film.
 3. The display deviceaccording to claim 1, wherein at least one of the anode and the cathodeis divided in a matrix form; an element-separating portion for isolatingat least adjacent ones of the thus discrete electrodes is formed betweenthe adjacent electrodes; and an element-separating portion coveringlayer is provided between the element-separating portion and the organiclayer.